1. Field of the Invention
The present invention relates to the mirror unit in a single lens reflex camera of the type which comprises a main mirror and a sub-mirror disposed behind the main mirror. When the main mirror is in the position for observation in which the operator can observe the object image formed on the finder screen through the finder, the sub-mirror directs the light transmitted through the semi-transparent part of the main mirror to the photo receiving element contained in a photo meter circuit or focus detecting circuit. When the main mirror is retracted to the position out of the photographing light path, the sub-mirror covers the semi-transparent part of the main mirror to prevent invert incident light coming from the finder part. More particularly, the present invention relates to an apparatus for driving and controlling the above sub-mirror.
2. Description of the Prior Art
There has been proposed an improvement relating to the above described type of apparatus which is the subject of a pending Japanese Utility Model Application No. 154,074/1977 owned by the same assignee as of the present application. FIG. 7, shows the arrangement of an apparatus disclosed in said prior Japanese Utility Model Application.
In FIG. 7, a main mirror is designated by 101 and a sub-mirror by 103. The main mirror 101 is supported by a supporting member 102 one end of which is supported on the camera housing rotatably about an axis. The sub-mirror 103 is supported by a supporting member 103 which is in turn supported pivotally on the main mirror supporting member 102. The sub-mirror supporting member 104 has an elongate slot 104a in which a pin 105a, provided on the free end of a swing lever 105 is engaged. The swing lever 105 is, at its other end, connected to a pivot for rotation and is under the biasing force of a spring 106. When the sub-mirror 103 is in the position for observation, the pin 105a of the swing lever 105 is pressed against the left side wall surface of the elongate slot 104a under the action of the spring 106 so as to hold the sub-mirror 103 in contact with a sub-mirror positioning pin 107. When the main mirror 101 is turned up clockwise to the position for photographing, the pin 105a of the swing lever 105 turns over its pressing side from the left side wall surface to the right side wall surface of the elongate slot 104a during the swing motion of the lever 105 so that the direction in which the sub-mirror 103 is biased by the spring 106 is reversed. When the main mirror 101 is moved to its retracted position for photographing as suggested by the phantom line in FIG. 7, the sub-mirror is brought into position to cover the semi-transparent part of the main mirror. This position of the sub-mirror is also suggested in phantom line. The sub-mirror is moved to this position by the biasing force of the spring 106 transmitted through the pin 105a which is pressing the right side wall surface of the slot 104a at that time.
As readily understood from the above, in the arrangement of FIG. 7, the biasing force of the spring 106 is transmitted to the sub-mirror 103 through the swing lever 105, the pin 105a thereon and the elongate slot 104a in which the pin is engaged. This arrangement is complicated in structure and requires an extremely high accuracy in machining the parts of the apparatus. Without such high precision there is assured no correct interlocking motion of the main and sub mirrors 101 and 103. This requirement of very high precision has resulted in low productivity which constitutes an important disadvantage of the prior art apparatus.